Dual-layer magnetic medium with nonhalogenated binder system

Abstract

A dual-layer magnetic recording medium including a non-magnetic substrate having a front side and a back side, a lower support layer formed over the front side and a magnetic upper recording layer formed over the lower layer comprising at least one magnetic particle pigment formed over said lower support layer, at least one of said layers of the front coating comprising a polymer binder system for the pigment, such binder system comprising a hard resin component and a soft resin component, wherein the soft resin component comprises a polyurethane polymer, and the hard resin component comprises a nonhalogenated vinyl copolymer comprising a plurality of pendent nitrile groups, a plurality of pendent hydroxyl groups, and at least one pendent dispersing group.

What is claimed is:  
     
         1 . A dual-layer magnetic recording medium comprising a non-magnetic substrate having a front side and a back side, a front coating on said substrate comprising a lower support layer formed over the front side and a magnetic upper recording layer comprising at least one magnetic particle pigment formed over said lower support layer, at least one of said layers of said front coating comprising a polymer binder system for the pigment, said binder system comprising a hard resin component and a soft resin component, wherein said soft resin component comprises a polyurethane polymer, and said hard resin component comprises a nonhalogenated vinyl copolymer comprising a plurality of pendent nitrile groups, a plurality of pendent hydroxyl groups, and at least one pendent dispersing group.  
     
     
         2 . A dual-layer magnetic recording medium according to  claim 1 , wherein said magnetic upper layer comprises said polymer binder system.  
     
     
         3 . A dual-layer magnetic recording medium according to  claim 1 , wherein said lower support layer comprises said polymer binder system.  
     
     
         4 . A dual-layer magnetic recording medium, wherein both said magnetic upper layer and said lower support layer comprise a polymer binder system according to  claim 1 .  
     
     
         5 . A dual-layer magnetic recording medium according to  claim 1 , wherein said polymer binder system comprises a polyurethane polymer having a glass transition temperature of less than about 60° C., and said hard resin component comprises a nonhalogenated vinyl copolymer comprising a plurality of pendent nitrile groups, a plurality of pendent hydroxyl groups, and at least one pendent dispersing group.  
     
     
         6 . A dual-layer magnetic recording medium according to  claim 5 , wherein the said hard resin component is a nonhalogenated vinyl copolymer of monomers comprising from about 5 to about 40 parts of (meth)acrylonitrile, from about 30 to about 80 parts of a nonhalogenated, nondispersing vinyl monomer, from about 1 to about 15 parts of a nonhalogenated, hydroxyl functional, vinyl monomer, and from about 0.125 to about 10 parts by weight of a nonhalogenated vinyl monomer bearing a dispersing group.  
     
     
         7 . A dual-layer magnetic recording medium according to  claim 1 , wherein the magnetic pigment particles have a coercivity of at least about 2000.  
     
     
         8 . A dual-layer magnetic recording medium according to  claim 1 , wherein the magnetic pigment particles have a coercivity of at least about 2300.  
     
     
         9 . A dual-layer magnetic recording medium according to  claim 1 , wherein the magnetic pigment particles have an average length no greater than about 100 nm.  
     
     
         10 . A dual layer magnetic recording medium according to  claim 1 , wherein the magnetic pigment particles have an average length no greater than about 80 nm.  
     
     
         11 . A dual layer magnetic recording medium according to  claim 1 , wherein the upper layer comprises a primary ferromagnetic pigment, aluminum oxide, a spherical large particle carbon material, a polyurethane binder, a nonhalogenated vinyl copolymer binder, a hardener, a fatty acid ester lubricant, and a fatty acid lubricant.  
     
     
         12 . A dual-layer magnetic recording medium according to  claim 1 , wherein said lower support layer comprises a pigment powder selected from a non-magnetic or soft magnetic powder having a coercivity of less than about 300 Oe, and a polymer binder system therefor.  
     
     
         13 . A dual-layer magnetic recording medium according to  claim 12 , wherein said polymer binder system for said lower support layer further comprises a nonhalogenated vinyl copolymer.  
     
     
         14 . A dual-layer magnetic recording medium according to  claim 12 , wherein said lower support layer further includes a fatty acid ester lubricant, a fatty acid lubricant, and a conductive carbon black material dispersed in said binder.  
     
     
         15 . A dual-layer magnetic recording medium according to  claim 12 , wherein said conductive carbon black comprises less than about 12 weight percent of said lower layer.  
     
     
         16 . A dual-layer magnetic recording medium according to  claim 1 , further comprising a back coat coated on said back side of said substrate.  
     
     
         17 . A dual-layer magnetic recording medium according to  claim 16 , wherein the back coat includes a carbon black pigment, a polyurethane binder, and at least one compound selected from phenoxy resin and nitrocellulose.  
     
     
         18 . A magnetic recording medium according to  claim 17 , wherein the back coat further comprises carbon black, and a metal oxide selected from titanium dioxide, iron oxide, aluminum oxide, and a mixture thereof.